Where have my objects camara and lights gone?
You have set a view clipping border. This allows you to only see a portion of the scene for clarity, as this cuts through objects it is also good for seeing inside an object.

The small dark area you have is the visible area in the viewport, as none of your objects are in there, you don't see anything.

You set the clipping border with &#9095; AltB and drag a rectangle over the area you want to see. Pressing &#9095; AltB again will clear it.

Also if you turn off the Load UI option when opening the blend file, the existing border will not be loaded.